The present invention is a method for monitoring a condition of a lubricant. The invention has particular benefit for monitoring fuel content, commonly referred to as fuel dilution, of an engine lubricant and in determining when a lubricant can no longer provide desired engine performance and life.
Lubricating oil is critical to the performance and operational life of an internal combustion engine. When the lubricant has appropriate viscosity for the required hydrodynamic film, detergents and dispersants to suspend and/or neutralize undesired contaminants, and surface active chemicals to protect engine component surfaces, the lubricant allows for long, efficient engine operation by reducing friction, wear and corrosion of engine components. In general, a lubricant's performance characteristics change with use and age, and a lubricant reaches the end of its useful life when any one of the lubricant's performance properties is out side a desired range. Using a lubricant past the end of its useful life reduces engine performance and life, possibly catastrophically.
Most often a lubricant reaches end-of-life due to normal consumption, degradation or depletion of base oil and/or additives by an engine in good condition, operating under a typical duty cycle and in a proper environment for an application. A lubricant, however, can also reach end-of-life due to abnormal engine condition, operating cycle and/or operating environment. An example of an abnormal engine condition is a fouled fuel injector that, instead of spraying a fine mist of fuel into a cylinder, either pre- or post-combustion, sprays an abnormal amount of fuel onto the cylinder wall. Fuel sprayed onto the cylinder wall can mix with a thin protective lubricant layer, thereby contaminating the lubricant with fuel. Fuel dilution degrades performance of the lubricant, which reduces the lubricant's useful life.
An engine operator wants to maximize the lubricant value by allowing the lubricant to remain in an engine and to not be replaced with fresh, i.e. unused, lubricant until the lubricant is near or at the end of its useful life. However, with the complexity of lubricant degradation, due to both normal and abnormal variables, accurate determination of the lubricant's condition has traditionally required off-line laboratory tests. Most operators, however, do not consider such test to be cost and/or time effective and instead choose to estimate lubricant condition when making a lubricant change decision. Change intervals are often based on operation parameters that are easily measured by the operator, such as time of operation, distance driven, and/or fuel use. Many engine manufacturers have developed algorithms to help operators make a change decision based on one or more engine operating parameters that may not easily be monitored by the operator. In either case, no actual lubricant condition information is used, and the change interval may not be optimized even for normal lubricant degradation modes, and is generally accepted to not be optimized if abnormal lubricant degradation occurs from, for example fuel dilution.
Recently, sensors for real-time, on-board measurement of a lubricant's electrical, optical or other properties have been introduced; see “Determining Proper Oil and Filter Change Intervals: Can Onboard Automotive Sensors Help?”, Sabrin Khaled Gebarin and Jim Fitch, Practicing Oil Analysis, March-April 2004. Many of these sensors provide an output that is a function of a measured lubricant property with no actual analysis of the fluid condition. In general, sensors without condition analysis are of limited value to engine or equipment manufacturers. To overcome this limitation, some sensors attempt to provide a complete solution with hardware and/or software that interpret fluid condition based on a measured property. The method disclosed in Lvovich, et al., U.S. patent application Ser. No. 10/271,885, provides a cost effective, relatively complete fluid condition analysis based on a multitude of a fluid's electrical impedance responses. While this method has been shown effective in determining when a lubricant reaches end-of-life under normal lubricant degradation, the method, except for a water/coolant leak, does not determine if end-of-life occurred due to an abnormal event. Electrical impedance methods, do not determine if end-of-life was primarily due to fuel dilution, or identify that fuel dilution is occurring before reaching end-of-life.
There remains a need for a cost-effective, on-line, lubricant monitoring sensor to provide a real-time determination if fuel dilution is occurring in order that the lubricant and the equipment using the lubricant can be maintained to provide desired performance and life.
The present invention provides a sensor and method for on-line determining lubricant condition based on a property that is consistent with fuel content while the lubricant is in use in industrial or transportation applications.